D.B.
It's so miserable to be backed up, and she needs some help right now. Go to the drug store and buy some Fleet enemas. Use vaseline on the tip, lay her in the floor of the bathroom and give her one of the enemas. Have her hold it as long as she can stand within the directions, then have her sit on the toilet without pushing until she absolutely HAS to. It will get some of it out, and maybe all of it, if the pieces aren't too big (so sorry that this is so graphic.) If she can't get it all out, tomorrow, try the other enema that comes in the box.
Now, every afternoon after she gets home from school, give her 3 bite sized prunes. No more than that until she gets used to them. Have her eat foods that have a lot of fiber in them - google her favorite foods and see how much fiber is in them - I 'll bet what she eats has very little fiber.
You need to incorporate ingredients into her food that has fiber in it. And she needs to drink a lot of water to make the fiber work. WIthout the water, the fiber isn't going to help her bowels.
You can go to a specialist (pediatric gastroenterologist), but it takes a while to get an appointment. You need to help her now. Enemas should ONLY be used once in a blue moon, but if you start putting some real changes in her eating habits, she might stop going through this sooner rather than later.
Good luck!
Dawn